CO2 Electroreduction Reaction Research Articles

Shear Field-Controlled Synthesis of Nitrogen-Doped Carbon Nanochains Forest with High-Density sp3 Defects for Efficient CO2 Electroreduction Reaction.

Defect engineering and nitrogen doping being effective strategies for modulating the surface chemical state of the carbon matrix have been widely explored to promote the catalytic activity in the territory of electrochemical energy storage and conversion devices. However, the controllable synthesis of carbon material with high-density specific defects and high nitrogen doping is still full of challenges. Here, we first synthesize one-dimensional necklace-like nitrogen-doped carbon nanochains (N-CNCs) with abundant defects on carbon fiber paper (CFP) by chemical vapor deposition (CVD) method. The resultant nanostructures are a bunch of interconnected carbon spheres with a hollow structure at the internode and present the complete one-dimensional nanochain configuration. Specifically, the N-CNCs with a corrugated surface possesses high content of sp3 defects (31.2%) and nitrogen (23.6 at %). Combining finite element analysis and experimental results, it reveals that the robust shear field generated by etching gas releasing from thermal decomposition of melamine in situ modulates the CVD process via changing the size and force environment of the metal catalyst droplets for formation of N-CNCs. Benefiting from the high ratio of sp3/sp2 and nitrogen doped on the surface, the N-CNCs@CFP displays a superior electrocatalytic performance for CO2RR, delivering CO Faradaic efficiency of 95.9% and a current density of 23.2 mA cm-2 at -0.86 V vs RHE. This work provides promising synthesis strategy and some inspirations for construction of ultradense and specific defects coupling with nitrogen doping sites into carbon materials to achieve high-efficiency electrocatalysis applications.

High-Entropy La(FeCuMnMgTi)O3 Nanoparticles as Heterogeneous Catalyst for CO2 Electroreduction Reaction.

In this work, La(FeCuMnMgTi)O3 HEO nanoparticles with a perovskite-type structure are synthesized and used in the electrocatalytic CO2 reduction reaction (CO2RR). The catalyst demonstrates high performance as an electrocatalyst for the CO2RR, with a Faradaic efficiency (FE) of 92.5% at a current density of 21.9 mA cm-2 under -0.75 V vs a saturated calomel electrode (SCE). Particularly, an FE above 54% is obtained for methyl isopropyl ketone (C5H10O, MIPK) at a partial current density of 16 mA cm-2, overcoming all previous works. Besides, the as-prepared HEO catalyst displays robust stability in the CO2RR. The excellent catalytic performance of La(FeCuMnMgTi)O3 is ascribed to the synergistic effect between the electronic effects associated with five cations occupying the high-entropy sublattice sites and the oxygen vacancies within the perovskite structure of the HEO. Finally, DFT calculations indicate that Cu plays a vital role in the catalytic activity of the La(FeCuMnMgTi)O3 HEO nanoparticles toward C2+ products.

Mesoporous Cu2O microspheres for highly efficient C2 chemicals production from CO2 electroreduction

Production of C2 chemicals (such as C2H4, C2H5OH, etc.) from CO2 electroreduction reaction (CO2ER) has been regarded as a promising route to solve the environmental problems and energy crisis. In this work, mesoporous Cu2O microspheres of ca. 700 nm diameter size with low crystallinity were fabricated to enable efficient conversion of CO2 to C2 chemicals by electrocatalytic reduction. It is revealed that compared with bulk Cu2O, the obtained mesoporous Cu2O microspheres have larger surface area, more grain boundaries and defects (unsaturated coordination sites), which facilitate the adsorption and stabilization of the important intermediates, such as *CO, on the route to C2 chemicals formation. As a result, the Faraday efficiency (FE) of C2 products reaches as high as 82.6 % and 78.5 % in an H-cell and a flow cell, respectively. In situ Raman and FT-IR spectra reveal that during CO2ER test there exists abundant *CO on the mesoporous Cu2O surface, thus increasing the opportunity of CC coupling. And the high coverage of *CO on catalyst surface during CO2ER protects and stabilizes the oxidation state of Cu species. This work demonstrates an effective strategy to introduce mesoporous structures and decreased crystallinity for improving the performance of CO2ER to C2 products.

Modulating local environment for electrocatalytic CO2 reduction to alcohol

The fundamental drivers for the selective CO2 electroreduction reaction (CO2RR) to alcohol (e.g. C2H5OH) or alkene (e.g. C2H4) still remain unexplored. Previous studies mainly focus on catalyst engineering to enhance electrocatalytic performance, while the selectivity to alcohol has reached a bottleneck. Here, we modulate local environment to reveal the contribution of *CO and *H reaction intermediates in the selectivity of CO2 to alcohol/alkene on Cu electrocatalyst. Through modifications on local CO2 concentration, varied *CO/*H coverage ratios can be achieved. Based on the reaction kinetics analysis, we find that there is a direct connection between local CO2 concentration and interfacial *CO and *H coverage, which finally affects the selectivity of CO2 to alcohol or alkene. To verify this principle, polyvinylidene fluoride (PVDF), a hydrophobic binder, were selected and introduced into the catalyst surface for further enhancement of interfacial *CO/*H coverage. With PVDF decoration, alcohol/alkene ratio increased from 0.69 to 1.35. The Faradic Efficiency of alcohol is up to 37.5 % under a high current density of 800 mA cm–2 (a partial current density of 300 mA cm–2), surpassing most reported Cu-based materials. Our findings provide a fundamental guidance for CO2RR to alcohol under an industrial-level current density.

Highly coordinated Ni-N5 sites for efficient electrocatalytic CO2 reduction toward CO with faradaic efficiency exceeding 99%

Electrochemical production of high value-added CO from CO2 on transition metal-nitrogen-carbon (M−N−C) catalysts is a promising approach to achieve carbon neutral economy, yet the quest for robust catalysts is driven by achieving > 96 % CO faradaic efficiency (FE) under low overpotential and wide potential range. Herein, we report a novel synthetic approach involving post-metallization of the pre-synthesized N-doped carbon (NC-T) support for the fabrication of robust and efficient Ni@NC-T quasi-molecular catalysts toward CO2 electroreduction reaction (CO2RR). The optimum Ni@NC-1100 catalyst exhibited an extremely high FECO > 99 % at −0.72 V vs. reversible hydrogen electrode (RHE). Of interest is the FECO maintained above 96 % over a wide potential window from −0.52 V to −1.12 V. Density functional theory (DFT) calculation validated that the presence of axial pyrrolic-N significantly enhances the Ni-N5 active site for CO2 activation, resulting in the lowest activation energy for the *COOH intermediate generation compared to other axial ligands.

A Unique Amorphous Porous BiSbOx Nanotube with Abundant Unsaturated Sb‐Stabilized BiO8−x Sites for Efficient CO2 Electroreduction in a Wide Potential Window

AbstractThe CO2 electroreduction reaction using sustainable electricity emerges as a viable strategy to produce high‐value‐added and profitable chemicals. The achievement of superior activity at a lower overpotential and higher selectivity in a wide potential window is vitally important for large‐scale industrial applications. Herein, a carbon‐composite amorphous porous BiSbOx nanotube with abundant unsaturated sites is reported to boost the conversion of CO2 to formate, exhibiting a formate selectivity of >90% in an extremely broad range of potentials from −0.5 to −1.4 V versus reversible hydrogen electrode (RHE) and a maximal energy conversion efficiency of 77.1%. Importantly, pure formic acid solution is directly obtained in a solid‐electrolyte cell for industrial‐scale applications. The porous tubular structure can expose more catalytic active sites, accelerate the mass transfer, and show fast surface charge transfer. Moreover, the unique coordination‐unsaturated Sb‐stabilized BiO8−x site can not only enhance the adsorption and activation of CO2 but also reasonably balance the stabilization and hydrogenation of *OCHO intermediate, thus leading to its obviously higher catalytic performance. As a result, a novel amorphous porous BiSbOx nanotube is successfully designed for efficient CO2 electroreduction, which may shed new light on developing many more amorphous composite metal oxide catalysts for conversion of inert small molecules.

Interfacial Electronic Interaction in Amorphous-Crystalline CeOx -Sn Heterostructures for Optimizing CO2 to Formate Conversion.

Formate, a crucial chemical raw material, holds significant promise for industrial applications in the context of CO2 electroreduction reaction (CO2 RR). Despite its potential, challenges, such as poor selectivity and low formation rate at high current densities persist, primarily due to the competing hydrogen evolution reaction (HER) and high energy barriers associated with *OCHO intermediate generation. Herein, one-step chemical co-reduction strategy is employed to construct an amorphous-crystalline CeOx -Sn heterostructure, demonstrating remarkable catalytic performance in converting CO2 to formate. The optimized CeOx -Sn heterostructures reach a current density of 265.1mAcm-2 and a formate Faraday efficiency of 95% at -1.07V versus RHE. Especially, CeOx -Sn achieves a formate current density of 444.4mAcm-2 and a formate production rate of 9211.8µmolh-1 cm-2 at -1.67V versus RHE, surpassing most previously reported materials. Experimental results, coupled with （density functional theory）DFT calculations confirm that robust interface interaction between CeOx and Sn active center induces electron transfer from crystalline Sn site to amorphous CeOx , some Ce4+ of CeOx get electrons and convert to unsaturated Ce3+ , optimizing the electronic structure of active Sn. This amorphous-crystalline heterostructure promotes electron transfer during CO2 RR, reducing the energy barrier formed by *OCHO intermediates, and thus achieving efficient reduction of CO2 to formate.

Modulating CO2 electroreduction to syngas by protic-nonprotic ionic liquid composite electrolytes

CO2 electroreduction reaction (CO2RR) to syngas with a tunable CO/H2 ratio and high current density is a promising but challenging application. Here, we report a novel electrolyte, including protic ionic liquid (IL) [Bim][NTf2], nonprotic IL, acetonitrile (MeCN) for CO2RR to syngas. When the concentration of [Bim][NTf2] increased from 0.005 to 0.12 mol·L-1, the CO/H2 ratio dropped from 30 to 0.1 and the current density increased from 26.4 to 113.4 mA·cm-2 at -2.3 V vs. Ag/Ag+ in H-cell. The [Bim][NTf2] not only can generate H+ to accelerate HER, but also increases the CO2 solubility to promote CO2RR to CO. Meanwhile, the [Bmim][NTf2] mainly increased the current density for CO2RR. By varying the concentration of [Bim][NTf2], the CO/H2 ratio could be modulated in ternary electrolyte. This work offers a novel method to modulate the CO/H2 ratio for enhancing the efficiency of CO2RR to syngas with a high current density in H-cell.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde

AbstractElectrochemical CO2 reduction can convert CO2 to value‐added chemicals, but its selectivity toward C3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO2 to propionaldehyde. Using Cu(OH)2 nanowires as the precatalyst, CO2/H2O is reduced to concentrated C2H4, CO, and H2 gases in a zero‐gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium‐phosphine complexes. The best candidate is identified to be the one with the 1,4‐bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close‐to‐atmospheric pressure. By coupling and optimizing the upstream CO2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C3 oxygenate selectivity of 44 % based on reduced CO2. These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde.

Electrochemical CO2 reduction can convert CO2 to value-added chemicals, but its selectivity toward C3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO2 to propionaldehyde. Using Cu(OH)2 nanowires as the precatalyst, CO2 /H2 O is reduced to concentrated C2 H4 , CO, and H2 gases in a zero-gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium-phosphine complexes. The best candidate is identified to be the one with the 1,4-bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close-to-atmospheric pressure. By coupling and optimizing the upstream CO2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C3 oxygenate selectivity of 44 % based on reduced CO2 . These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.

Engineering Copper‐Based Covalent Organic Framework Microenvironments to Enable Efficient CO2 Electroreduction with Tunable Ethylene/Methane Switch

AbstractA microenvironment engineering strategy has been developed to switch the CO2 electroreduction reaction (CO2RR) selectivity from methane (CH4) to ethylene (C2H4) by adjusting the coordination microstructures of trinuclear copper cluster‐based metal‐covalent organic framework (MCOF). When Cu sites are oriented to channels in Cu‐PyCA‐MCOF, methane is the main product. Conversely, when trinuclear copper sites are coordinated with OH− and H2O molecules in Cu‐PyCAOH‐MCOF nanosheets, the main product switches from CH4 to C2H4 with 50.5% selectivity and 200.2 mA cm− partial current density at −1.2 V (vs RHE). This happens because CO2 molecules can only contact active sites perpendicular to the trinuclear copper cluster plane in Cu‐PyCAOH‐MCOF nanosheets, where the Cu─Cu distance between them is 3.2 Å, favoring the efficient conversion of CO2 to C2H4 through the C─C coupling reaction. Operando infrared spectroscopy, in situ X‐ray absorption near‐edge structure spectra, and DFT calculations reveal that changing the coordination environments of MCOFs significantly stabilizes key intermediates and reduces the energies of the CO2RR. This work offers an effective strategy for enhancing CO2RR performance toward C2H4 products by tuning the microenvironments of copper‐based electrocatalysts.

Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate-containing Electrolyte for Highly Active Electrocatalytic CO2 Reduction to Formate.

The catalyst-reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2 RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2 O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2 O2 CO3 /Bi2 O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2 O2 CO3 /Bi2 O3 heterostructure with strong electron interaction served as the highly active structure for CO2 RR, achieving a formate Faradaic efficiency of 98.1 % at -0.8 Vvs RHE . Theoretical calculations demonstrate that the significantly tuned p-orbit electrons of the Bi sites in Bi2 O2 CO3 /Bi2 O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure.

Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate‐containing Electrolyte for Highly Active Electrocatalytic CO2 Reduction to Formate

AbstractThe catalyst‐reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2O2CO3/Bi2O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2O2CO3/Bi2O3 heterostructure with strong electron interaction served as the highly active structure for CO2RR, achieving a formate Faradaic efficiency of 98.1 % at −0.8 Vvs RHE. Theoretical calculations demonstrate that the significantly tuned p‐orbit electrons of the Bi sites in Bi2O2CO3/Bi2O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure.

Scale‐up of electrochemical flow cell towards industrial CO2 reduction to potassium formate

AbstractThe CO2 electroreduction reaction (CO2RR) presents a pathway to decarbonize the manufacturing industry by using clean electricity and CO2 as feedstocks instead of relying on fossil fuels. Although known for over 100 years, this technology has yet only been developed at bench‐top scale (1–100 cm2). In this manuscript, we report CO2 electroreduction to potassium formate (HCOOK) in a stack of two 1526‐cm2 three‐compartments electrochemical cells with gas diffusion electrode (GDE) cathodes. In this stack, we achieved over 60 % current selectivity towards HCOOK at current densities of 200 mA cm−2 and under cell voltages of ~4.0 V. We reached these performance metrics by tuning electrolyte composition and cell architecture. We also show that a minimum of +10‐14 kPa of pressure difference must be applied between gaseous and catholyte compartments to enable the CO2RR to take place. We emphasize the challenges associated with scaling‐up a CO2 electrochemical cell, specifically by demonstrating that optimal operation parameters are strongly correlated to cell architecture. This study demonstrates the feasibility of developing CO2RR electrochemical cells to an industrial scale.

Gas diffusion enhanced electrode with ultrathin superhydrophobic macropore structure for acidic CO2 electroreduction

Carbon dioxide (CO2) electroreduction reaction (CO2RR) offers a promising strategy for the conversion of CO2 into valuable chemicals and fuels. CO2RR in acidic electrolytes would have various advantages due to the suppression of carbonate formation. However, its reaction rate is severely limited by the slow CO2 diffusion due to the absence of hydroxide that facilitates the CO2 diffusion in an acidic environment. Here, we design an optimal architecture of a gas diffusion electrode (GDE) employing a copper-based ultrathin superhydrophobic macroporous layer, in which the CO2 diffusion is highly enhanced. This GDE retains its applicability even under mechanical deformation conditions. The CO2RR in acidic electrolytes exhibits a Faradaic efficiency of 87% with a partial current density (jC2+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$( {j}_{{{{\\rm{C}}}}_{2+}})$$\\end{document} of −1.6 A cm−2 for multicarbon products (C2+), and jC2+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {j}_{{{{{{\\rm{C}}}}}}_{2+}}$$\\end{document} of −0.34 A cm−2 when applying dilute 25% CO2. In a highly acidic environment, C2+ formation occurs via a second order reaction which is controlled by both the catalyst and its hydroxide.

Highly selective electrocatalytic reduction of CO2 to ethane over a petal-like Zn(OH)2/Cu2+1O/Cu foam catalyst at low overpotentials

Due to multiple reaction steps and a lack of efficient catalysts, the synthesis of ethane from the CO2 electroreduction reaction (ECO2RR) is particularly challenging. A Zn(OH)2/Cu2+1O/CF catalyst was applied in electrocatalytic CO2 reduction to ethane, which offers high selectivity at low overpotentials.

Surface reconstruction of copper foil via electrochemical etching to proliferate CH4 production from CO2 electroreduction

Electrocatalytic CO2 reduction (eCO2R) to CH4 is a prospective approach for producing high value-added fuels. In this work, an effective approach was proposed by surface reconstruction using copper foil to facilitate eCO2R to CH4. The copper foil surface reconstruction was achieved via electrochemical etching in dilute phosphoric acid. Comprehensive characterizations suggested that the crystallinity and chemical binding energy states of the copper foil were well preserved after surface reconstruction, but the arrangement of copper atoms on the surface was adjusted. Etching time for 80 s was the most preferable condition, obtaining a uniform valley pattern structure with abundant grain boundaries, reporting the highest CH4 Faraday efficiency of 68.84% which was an order of magnitude higher compared to green foil counterpart. The relevant partial current density, CH4 production rate, and half-cell power conversion energy were measured to be −16.32 mA cm−2, 0.174 μmol s−1 cm−2, and 28.8% respectively from eCO2R at −1.3 V (vs. RHE). The in-situ ATR-IR spectroscopy confirmed that the surface reconstructed copper foil can significantly strengthen the adsorption of the *CO intermediate, facilitating its further hydrogenation to produce CH4 instead of dimerization to give C2 products. This work expanded the method of surface modification for copper foil via electrochemical etching and realized the regulation of geometric morphology on catalyst surface to obtain the desired performance for CO2 electroreduction reaction.

Positively charged nickel-sulfur dual sites for efficient CO2 electroreduction reaction

Electrochemical CO2 reduction (CO2RR) into chemicals and fuels has gained great interest, but is subjected to low current density and poor product selectivity. Here a theory-guided design of sulfur-doped single nickel atom catalyst (Ni-SAC/SNC) with the optimal Ni-S dual active configuration was present for efficient CO2RR. Experiments combined with theory verified that the positively charged Ni-S dual sites drastically promoted the electronic localization of Ni center, which improved the stabilization of key COOH* intermediate and thus boosted CO production on Ni. This catalyst exhibited a high CO Faradaic efficiency of ∼98% and a current density of ∼32.5 mA cm−2 at a low overpotential of 620 mV, which exceeded most of single-atom electrocatalysts. This work offers atomic-level insights into the correlation between the electronic density of atomic sites and CO2RR performance, promoting the theory-guided rational design of efficient catalysts.

Substrate interaction of graphene quantum dots in solution studied by hyperpolarized NMR

The reversible adsorption of CO2-derived species to graphene quantum dots in CO2 electroreduction reaction was characterized by nuclear spin hyperpolarized NMR. Hyperpolarization of 13C-labeled sodium bicarbonate by the dissolution dynamic nuclear polarization (DNP) technique provided a 5000-fold signal enhancement and enabled real-time and in-situ 13C NMR experiments. The R1 and R2 relaxation rates were measured using time-resolved DNP-NMR experiments, and the bound species were confirmed to be carbonic acid and its conjugates. A significant difference in the relaxation rates of bound and free species was found, indicating a reversible binding. In addition to relaxation rates, kinetic rate constants were fitted from the small-flip angle experiments and compared to theoretical calculations. The pH-dependent adsorption and desorption rate constants were found in the range of 3.5–9.5 and 0.7–2.0 s−1, with the average binding distance at 279 - 291 pm. The DNP-NMR technique was demonstrated as an effective way to study surface adsorption, with potential in electrochemistry and kinetics applications.

Continuous constant potential model for describing the potential-dependent energetics of CO2RR on single atom catalysts.

In this work, we have proposed a Continuous Constant Potential Model (CCPM) based on grand canonical density functional theory for describing the electrocatalytic thermodynamics on single atom electrocatalysts dispersed on graphene support. The linearly potential-dependent capacitance is introduced to account for the net charge variation of the electrode surface and to evaluate the free energetics. We have chosen the CO2 electro-reduction reaction on single-copper atom catalysts, dispersed by nitrogen-doped graphene [CuNX@Gra (X = 2, 4)], as an example to show how our model can predict the potential-dependent free energetics. We have demonstrated that the net charges of both catalyst models are quadratically correlated with the applied potentials and, thus, the quantum capacitance is linearly dependent on the applied potentials, which allows us to continuously quantify the potential effect on the free energetics during the carbon dioxide reduction reaction instead of confining it to a specific potential. On the CuN4@Gra model, it is suggested that CO2 adsorption, coupled with an electron transfer, is a potential determining step that is energetically unfavorable even under high overpotentials. Interestingly, the hydrogen adsorption on CuN4@Gra is extremely easy to occur at both the Cu and N sites, which probably results in the reconstruction of the CuN4@Gra catalyst, as reported by many experimental observations. On CuN2@Gra, the CO2RR is found to exhibit a higher activity at the adjacent C site, and the potential determining step is shifted to the *CO formation step at a wide potential range. In general, CCPM provides a simple method for studying the free energetics for the electrocatalytic reactions under constant potential.